These plains correspond with those of the Mississippi and of Canada in the northern hemisphere. If one of their extremities approaches less nearly to the polar regions, the other enters much further into the region of palm-trees. That part of this vast basin extending from the eastern coast towards the Rio Paraguay does not present a surface so perfectly smooth as the part situated on the west and the south-east of the Rio de la Plata, and which has been known for ages by the name of Pampas, derived from the Peruvian or Quichua language.* (* Hatan Pampa signifies in that language, a great plain. We find the word Pampa also in Riobamba and Guallabamba; the Spaniards, in order to soften the geographical names, changing the p into b.) Geognostically speaking these two regions of east and west form only one basin, bounded on the east by the Sierra de Villarica or do Espinhaco, which loses itself in the Capitania of San Paul, near the parallel of 24 degrees; issuing on the north-east by little hills, from the Serra da Canastra and the Campos Parecis towards the province of Paraguay; on the west by the Andes of Upper Peru and Chile; and on the north-west by the ridge of the partition of the waters which runs from the spur of Santa Cruz de la Sierra, across the plains of the Chiquitos, towards the Serras of Albuquerque (latitude 19 degrees 2 minutes) and San Fernando. That part only of this basin lying on the west of the Rio Paraguay, and which is entirely covered with gramina, is 70,000 square leagues. This surface of the Pampas or Llanos of Manse, Tucuman, Buenos Ayres and eastern Patagonia is consequently four times greater than the surface of the whole of France. The Andes of Chile narrow the Pampas by the two spurs of Salta and Cordova; the latter promontory forms so projecting a point that there remains (latitude 31 to 32 degrees) a plain only 45 leagues broad between the eastern extremity of the Sierra de Cordova and the right bank of the river Paraguay, stretching in the direction of a meridian, from the town of Nueva Coimbra to Rosario, below Santa Fe. Far beyond the southern frontiers of the old viceroyalty of Buenos Ayres, between the Rio Colorado and the Rio Negro (latitude 38 to 39 degrees) groups of mountains seem to rise in the form of islands in the middle of a muriatiferous plain. A tribe of Indians of the south (Tehuellet) have there long borne the characteristic name of men of the mountains (Callilehet) or Serranos. From the parallel of the mouth of the Rio Negro to that of Cabo Blanco (latitude 41 to 47 degrees) scattered mountains on the eastern Patagonian coast denote more considerable inequalities inland. All that part, however, of the Straits of Magellan, from the Virgins' Cape to the North Cape, on the breadth of more than 30 leagues, is surrounded by savannahs or Pampas; and the Andes of western Patagonia only begin to rise near the latter cape, exercising a marked influence on the direction of that part of the strait nearest the Pacific, proceeding from south-east to north-west.
If we have given the plains or great basins of South America the names of the rivers that flow in their longitudinal furrows, we have not meant by so-doing to compare them to mere valleys. In the plains of the Lower Orinoco and the Amazon all the lines of the declivity doubtless reach a principal recipient, and the tributaries of tributary streams, that is the basins of different orders, penetrate far into the group of the mountains. The upper parts or high valleys of the tributary streams must be considered in a geological table as belonging to the mountainous region of the country, and beyond the plains of the Lower Orinoco and the Amazon. The views of the geologist are not identical with those of the hydrographer. In the basin of the Rio de la Plata and Patagonia the waters that follow the lines of the greatest declivities have many issues. The same basin contains several valleys of rivers; and when we examine nearly the polyedric surface of the Pampas and the portion of their waters which, like the waters of the steppes of Asia, do not go to the sea, we conceive that these plains are divided by small ridges or lines of elevation, and have alternate slopes, inclined, with reference to the horizon, in opposite directions. In order to point out more clearly the difference between geological and hydrographic views, and to prove that in the former, abstracting the course of the waters which meet in one recipient, we obtain a far more general point of view, I shall here again recur to the hydrographic basin of the Orinoco. That immense river rises on the southern slope of the Sierra Parime. It is bounded by plains on the left bank, from the Cassiquiare to the mouth of the Atabapo, and flows in a basin which, geologically speaking, according to one great division of the surface of South America into three basins, we have called the basin of the Rio Negro and the Amazon. The low regions, which are bounded by the southern and northern declivities of the Parime and Brazil mountains, and which the geologist ought to mark by one name, contain, according to the no less precise language of hydrography, two basins of rivers, those of the Upper Orinoco and the Amazon, separated by a ridge that runs from Javita towards Esmeralda. From these considerations it results that a geological basin (sit venia verbo) may have several recipients and several emissaries, divided by small ridges almost imperceptible; it may at the same time contain waters that flow to the sea by different furrows independent of each other, and the systems of inland rivers flowing into lakes more or less charged with saline matter. A basin of a river, or hydrographic basin, has but one recipient, one emissary; if, by a bifurcation, it gives a part of its waters to another hydrographic basin, it is because the bed of the river, or the principal recipient, approaches so near the banks of the basin or the ridge of partition that the ridge partly crosses it.
The distribution of the inequalities of the surface of the globe does not present any strongly marked limits between the mountainous country and the low regions, or geologic basins. Even where real chains of mountains rise like rocky dykes issuing from a crevice, spurs more or less considerable, seem to indicate a lateral upheaving. While I admit the difficulty of properly defining the groups of mountains and the basins or continuous plains, I have attempted to calculate their surfaces according to the statements contained in the preceding sheets.
TABLE OF AREAS FOR SOUTH AMERICA.
COLUMN 1 : GEOGRAPHICAL LOCATION.
COLUMN 2 : AREA IN SQUARE MARINE LEAGUES.
1. MOUNTAINOUS PART:
Andes : 58,900.
Littoral Chain of Venezuela : 1,900.
Sierra Nevada de Merida : 200.
Group of the Parime : 25,800.
System of the Brazil mountains : 27,600.